(Newser)
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To a casual observer, the plum-sized chunk of metal that rests inside a sealed, underground vault near Paris is unremarkable. But to scientists, the cylinder of platinum and iridium is one of the constants upon which science is based. It weighs exactly 1 kilogram, or at least it used to, reports the BBC.

Le Grand K, forged in 1880 along with several duplicates, and against which all kilograms in the world are measured, is losing weight. Or so it seems. Some scientists postulate the replicas may be gaining weight, about the mass of one grain of sugar so far. Needless to say, scientists are looking for a more constant constant to use.